Thousands of migrants who had been stuck for days in Southeastern Europe have started arriving in Austria after Hungary escorted them to the border.

Austrian police on September 19 reported 6,700 new arrivals from Hungary since midnight, amid deepening discord in Europe over the biggest westward migration in decades.

The development comes after thousands of migrants, many lacking food and water, were trapped in Southeastern Europe, in some cases for several days, after countries began putting up barriers that blocked their passage to Western Europe.

The migrant path was first blocked by Hungary, which sealed off its southern border with Serbia with a razor-wire fence and tough other measures to keep people out.

That caused a massive influx of more than 15,000 people over three days into Croatia, which could not cope and then began escorting people to the border with Hungary.

In response, Hungary transported the migrants to the border with Austria by bus and train.

WATCH: There were harrowing scenes on September 18 at Croatia's border with Serbia, as riot police tried to hold back thousands of refugees and migrants trying to find a new route to Western Europe. The Croatian government says at least 9,200 migrants have entered the country since Hungary closed its borders this week.

Meanwhile, Slovenia has blocked off its borders and used pepper spray on migrants late on September 18.